Water-cooled engines such as automotive engines have conventionally been using water (cooling water) as a medium for cooling the cylinders and cylinder head and have a fluid pump as a device for forcibly circulating the cooling water by feeding the cooling water to a water jacket formed within the cylinder block of the engine. Such a fluid pump is typically called “water pump,” and has a pump base configured from a part of the cylinder block and having an inlet port and an outlet port for the cooling water, a pump case attached to the pump base and configuring a pump chamber, a pump pulley supported rotatably in an outer circumferential portion of the pump case, a drive shaft that has one end portion coupled to the pump pulley and extends inside the pump chamber through a shaft hole of the pump case, a bearing for supporting the drive shaft rotatably, and an impeller attached to an end portion of the drive shaft and provided inside the pump chamber (see Japanese Laid-Open Patent Publication No. 2007-16629 (A), for example). Additionally, a variable fluid pump has been proposed in recent years in which an electromagnetic clutch is disposed in order to activate or deactivate the power transmission path between a pump pulley and a drive shaft, wherein the power transmission path is deactivated to limit supply of the cooling water when the engine is cool, and the power transmission path is activated to supply the cooling water when the engine is warm (see Japanese Laid-Open Patent Publication No. 2011-202526 (A), for example).
Such a water pump configured as described above is provided with sealing means for keeping the space between the shaft hole of the pump case and the drive shaft fluid-tight in order to keep the pump chamber sealed. As the sealing means, the one called “mechanical seal” configured from a first sealing member attached to the pump case and a second member attached to the drive shaft is usually used, wherein the both sealing members are brought into contact with each other to form a sealing surface.